It is VOIP I think, didn’t really investigate doing it myself. Zen transferred the number and my existing phones just plug into the router. It was all very straight forward.
That is certainly VoIP or digital voice as they call it. I have had VoIP for years, I use sipgate., I got it when I went to a wireless broadband service and I needed a home phone, so my Dad could phone me, also a friend at the time would not use a mobile.
I keep it because it is here now, saying that I still use it, and it is the only number my work has, I will not give them my mobile number.
If I went to zzoomm they have no landline, they can supply VoIP via something called KIT. And no it has nothing to do with a talking car

, anyway that has an extra T on.
Kit has a £9.99 a month rental, so I certainly would not bother with it, Sipgate I just top it up and for the amount of time I use it, it is fine.
i hope Zen works out for you, they are a bit too expensive for me to be honest.
Adrian
Desktop machine Ryzen powered with windows something or other.
Plusnet FTTC